PHP中Unicode编码转换为UTF-8字符

/**
* utf8字符转换成Unicode字符
* @param  [type] $utf8_str Utf-8字符
* @return [type]           Unicode字符
*/
function utf8_str_to_unicode($utf8_str)
{
$unicode = (ord($utf8_str[0]) & 0x1F) << 12;
$unicode |= (ord($utf8_str[1]) & 0x3F) << 6;
$unicode |= (ord($utf8_str[2]) & 0x3F);
return dechex($unicode);
}

/**
* Unicode字符转换成utf8字符
* @param  [type] $unicode_str Unicode字符
* @return [type]              Utf-8字符
*/
function unicode_to_utf8($unicode_str)
{
$code = intval(hexdec($unicode_str));
//这里注意转换出来的code一定得是整形，这样才会正确的按位操作
$ord_1 = decbin(0xE0 | ($code >> 12));
$ord_2 = decbin(0x80 | (($code >> 6) & 0x3F));
$ord_3 = decbin(0x80 | ($code & 0x3F));
$utf8_str = chr(bindec($ord_1)) . chr(bindec($ord_2)) . chr(bindec($ord_3));
return $utf8_str;
}